JP 2006-96218 A discloses an example of a hydraulic braking device that is capable of controlling a braking force with respect to a vehicle in cooperation with a regenerative braking device. The device is equipped with a brake actuator that adjusts a differential pressure between a master cylinder configured to generate a master cylinder pressure as a hydraulic pressure depending on a braking operation of a driver inside a master chamber and a wheel cylinder provided for a wheel. The brake actuator is a so-called inline type actuator that has a differential pressure regulating valve disposed in a pathway between the master cylinder and the wheel cylinder, and a supply pump that pumps up the brake fluid from the interior of the master chamber of the master cylinder and discharges the brake fluid to the pathway of the wheel cylinder side rather than the differential pressure regulating valve.
In such a hydraulic braking device, in order to give the braking force corresponding to a difference, which is obtained by subtracting the regenerative braking force applied to the vehicle by the regenerative braking device from the target braking force depending on an amount of braking operation of the driver, to the vehicle, a brake actuator is operated. It should be noted that the braking force applied to the vehicle by the hydraulic braking device will be referred to as “hydraulic braking force”.
Here, it is difficult to control the regenerative braking force applied to the vehicle by the regenerative braking device compared to the hydraulic braking force applied to the vehicle by the hydraulic braking device. For that reason, when the vehicle speed of the vehicle is lowered by the braking operation of the driver, and the vehicle speed becomes lower than the switching start speed, a so-called switching control is performed which gradually decreases the regenerative braking force and gradually increases the hydraulic braking force in accordance with a decrease in the vehicle speed. Moreover, when the vehicle speed reaches the switching termination speed greater than “0 (zero)”, since the regenerative braking force is “0 (zero)”, the switching control is terminated. Thereafter, the brake actuator is controlled so that the hydraulic braking force coincides with the required braking force depending on a braking operation of the driver.
Incidentally, when increasing the hydraulic braking force so as to compensate the decrease of the regenerative braking force in the above-described switching control, the brake actuator is actuated so that the differential pressure between the master cylinder and the wheel cylinder gradually increases. At this time, the brake fluid is pumped up from the interior of the master chamber of the master cylinder by the supply pump of the brake actuator and is supplied into the wheel cylinder. Then, a master piston moves in a direction of increasing the master cylinder pressure in accordance with a decrease in the brake fluid from the master chamber, and the operational reaction force acting on the brake pedal decreases. The operational reaction force is a force which acts on the brake pedal in an opposite direction to the braking operation force of the driver. For that reason, in a case where the braking operation force of the driver is approximately constant, when the operational reaction force decreases in this manner, a brake pedal drivingly connected to the master piston is displaced. That is, even if the driver himself does not increase the braking operation force, the brake pedal is displaced in the operating direction as a direction of increasing the master cylinder pressure, and there is a risk of a decrease in drivability.